1. Field of the Invention
The present invention relates to a vapor reflow type soldering method and an apparatus therefor by which soldering is effected by bringing a matter to be treated, which is prepared by mounting electronic components and the like on a circuit substrate applied with a solder, into contact with a saturated vapor of a thermomedium, and more particularly, to a vapor reflow type soldering method and a vapor reflow type soldering apparatus improved to be able to prevent water contained in the air from being mixed in the thermomedium.
2. Description of the Prior Art
In vapor reflow type soldering apparatus, soldering is effected in such a manner, as disclosed in Japanese Patent Unexamined Publication No. 60-106502, that a treated matter prepared by mounting electronic components and the like on a circuit substrate applied with a solder is carried into a saturated vapor of a thermomedium of a large specific gravity to air so as to be brought into contact with the saturated vapor so that the treated matter is heated by the latent heat of condensation of the saturated vapor to ensure the soldering. However, since a flux is generated at the time of soldering and mixed in the thermomedium, a filtering section is equipped for the purpose of removing the flux mixed in the thermomedium as disclosed in Japanese Patent Unexamined Publication Nos. 62-148086 and 63-90361.
In the above well-known vapor reflow type soldering apparatus, as a day's operation is finished, heating by a heater is stopped and, at the same time, the thermomedium is cooled by cooling coils to become liquid which is returned to a vapor tank and collected in the bottom portion thereof. As the thermomedium is condensed, air enters through a carrier inlet and a carrier outlet so that it is cooled by the cooling coils like the thermomedium, resulting in that water produced due to condensation of steam in the air is allowed to flow into the vapor tank together with the thermomedium. Further, since the thermomedium collected in the vapor tank is transferred to a filtering section, the interior of the vapor tank is filled up with the air. Thereafter, the thermomedium from which foreign matter is removed due to cooling in the filtering section is returned to the vapor tank to be made to come in contact with water in the air or water condensed on the inner wall of the vapor tank, resulting in the mixing with part of water.
The thermomedium transferred from the vapor tank to the filtering section is cooled by a cooling coil of the filtering tank. In this case, steam in the air entered into the upper portion of the filtering tank is condensed to be mixed into the thermomedium. Further, in case of transferring the thermomedium to the filtering tank, if there has already been generated condensate water in the cooling coil, this water is made to be mixed together into the thermomedium as well.
Since a fluoric inert liquid is used as the thermomedium, when the thermomedium is heated by the heater at the time of resuming the operation on the next day, the condensate water mixed in or being in contact with the thermomedium is first boiled to react with the thermomedium to generate hydrofluoric acid, resulting in some cases in the corrosion of the reflow section or the deterioration of the thermomedium. Further, in case that water is contained in the thermomedium, as the thermomedium is heated the water is boiled to absorb latent heat. As a result, not only the heating condition of the thermomedium becomes unstable but also extra energy is required.